Nanocrystalline Cu-ZnO as an Green Catalyst for One Pot Synthesis of 4,4'-((phenyl)methylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) Derivatives

Synthesis of 4,4'-((phenyl)methylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) derivatives was successively carried out using Cu doped ZnO nanomaterials. The nanocrystalline Cu-ZnO was obtained by decomposing as-synthesized copper-zinc oxalate intermediate at 520 °C. The prepared Cu-ZnO nanostructured catalyst was characterized with FTIR, X-ray diffraction, field emission scanning electron microscope and electron diffraction techniques. XRD analysis indicates the formation of highly crystalline hexagonal phase of ZnO along with the presence of monoclinic CuO. FESEM photographs shows the existence of plate like structures made up of small spherical shaped particles having size in the range of 30-50 nm. As-synthesized Cu-ZnO was used as heterogeneous catalyst for one pot synthesis of 4,4'-((phenyl)methylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol) derivatives using phenyl hydrazine, ethyl acetoacetate and aromatic aldehydes. The 3-methyl-1-phenyl-1H-pyrazol-5-ol was obtained as in-situ precursor to the series of bis-pyrazolone derivatives. The progress of reaction was monitored by thin layer chromatography. The obtained organic product was further characterized and confirmed by FT-IR, 1H-NMR, 13C-NMR and HRMS spectroscopic techniques. The Cu-ZnO catalyst confers upto 96% yield of pyrazolone derivatives in ethanol solvent at refluxing condition. The Cu-ZnO catalyst was used successfully up to 5 cycles without much loss of catalytic activity. Overall, the use of environmental friendly Cu-ZnO nano-structures as a heterogeneous catalyst shows higher yield and lower reaction time towards the synthesis of bispyrazolone derivatives by Tandem Knoevenagel/Michael reaction.